1. Field of the Invention
The present invention relates generally to a switched reluctance machine (SRM). The present invention relates more specifically to a SRM having a new relationship between the number of stator poles and rotor poles.
2. Discussion of the Related Art
A switched reluctance machine has salient poles on its stationary member stator and rotating member rotor. SRMs are advantageous in their operation because they do not require permanent magnets or field windings on the rotor. Because of simple and robust construction, fault tolerant capabilities and torque-speed characteristics, SRMs are very popular to provide auxiliary power in aircraft, automotive and vehicular systems, non-conventional energy sources, and other industrial machineries and equipments.
SRMs are realized in a variety of forms. In particular, the constructions differ in the number of stator and rotor poles on the stationary and movable members, respectively, and in the number of independent circuits with which the controller is separately able to switch stator windings in and out of circuit. The stator poles have phase windings on them while the rotor poles have no windings. Each set of windings separately switched in and out of circuit by the controller constitutes one phase of the machine. The machine may have one or more phases.
Torque produced by an SRM is function of the instantaneous phase inductance, and hence the instantaneous rotor position, and the stator coil currents. By nature of the machine characteristics and control strategy, maximum torque is produced when rotor & stator poles are unaligned, while minimum torque is produced at the aligned position. This results in considerable torque ripple and is one of the factors limiting the application of SRMs. For example, it is known that humans can sense very low levels of torque perturbation. There is therefore a desire in the art to minimize the problem of torque ripple, increase torque production, and otherwise improve the operation of SRMs.